Mark,
I can vouch for SASS Kit. I have some excellent custom-made stuff from them, specifically is my smock which I wear all the time when out and about.
They are very military orientated and as a result most of their items are mil-spec and designed for Survival / Evasion / Escape work so they are very compact and small - ideal for a PSK.
Also try
http://www.sofmilitary.co.uk as I have bought lots from them also and never had a problem. (They are called "Soldier of Fortune" but have no links with the magazine of the same name).
However, I quite often just type into a search engine the specific item I am looking for. For example, last night - after reading many a post on this forum, I decided I wanted a Photon III LED Light to try out so typed it into google.co.uk and it came up with clubbertoys.com as the cheapest, the site is meant to be for toys and 'accesories' for nightclub goers!!
Hope this helps,
Rich Fisher
PS As an afterthought, I have also bought stuff from
www.nomadtravel.co.uk and found it a useful site and very 'inspirational'